Simulating Subhalos at High Redshift: Merger Rates, Counts, and Types

TL;DR

This study uses high-resolution simulations to analyze the evolution and characteristics of galaxy mergers and subhalo interactions at high redshift, revealing differences from dark matter halo merger rates and satellite merger statistics.

Contribution

It provides new insights into the evolution of galaxy merger rates, satellite merger likelihoods, and the relationship between halo and galaxy merger histories at high redshift.

Findings

Galaxy merger rate evolves more slowly than dark matter halo merger rate at z>2.5.

15%-35% of recent mergers involve satellite galaxies.

Satellite halo occupation peaks at z~2.5 for fixed halo mass.

Abstract

Galaxies are believed to be in one-to-one correspondence with simulated dark matter subhalos. We use high-resolution N-body simulations of cosmological volumes to calculate the statistical properties of subhalo (galaxy) major mergers at high redshift (z=0.6-5). We measure the evolution of the galaxy merger rate, finding that it is much shallower than the merger rate of dark matter host halos at z>2.5, but roughly parallels that of halos at z<1.6. We also track the detailed merger histories of individual galaxies and measure the likelihood of multiple mergers per halo or subhalo. We examine satellite merger statistics in detail: 15%-35% of all recently merged galaxies are satellites and satellites are twice as likely as centrals to have had a recent major merger. Finally, we show how the differing evolution of the merger rates of halos and galaxies leads to the evolution of the average satellite occupation per halo, noting that for a fixed halo mass, the satellite halo occupation peaks at z~2.5.